Land use patterns skew sex ratios, decrease genetic diversity and trump the effects of recent climate change in an endangered turtle

Abstract

Aim Changes in both land use and climate can cause population declines and species extinctions, but the relative effects of these two stressors are often dependent on species‐specific life histories. Turtles are highly threatened as a taxonomic group and are particularly sensitive to environmental change due to their life history, habitat preferences and physiology. We used both sex data and genetic diversity across a landscape‐scale gradient in land use intensity and recent climate change to characterize the relative effects of these factors on three turtle species (including the endangered Blanding's turtle, Emydoidea blandingii) with different life histories and thus different vulnerabilities to environmental change. Location Wisconsin, USA. Methods Turtles were captured and sampled for genetic analyses at 18 sites. Sampled individuals were genotyped for species‐specific sets of microsatellite markers, and population‐level genetic diversity was assessed using rarefied allelic richness and heterozygosity. The relative effects of road density, public land area and recent climate change on genetic diversity and sex ratio were evaluated using regression methods and model‐selection criteria. Results Increased land use intensity was associated with male‐skewed sex ratios and decreased genetic diversity in E. blandingii but not co‐occurring species. Recent climate change did not explain variability in either sex ratio or genetic diversity for any of the three species examined. Main conclusions Changing land use has multiple impacts on turtle populations that are modulated by species‐specific life history traits. Extensive terrestrial movements associated with nesting in E. blandingii increase female vulnerability to road mortality, which in turn has led to declines in genetic diversity. The predicted effects of recent climate change may have been dampened by behavioural plasticity. We suggest that the disproportionate effect of land use on E. blandingii warrants greater legal protection for this species.

Climate change surpasses land-use change in the contracting range boundary of a winter-adapted mammal

“…However, if habitat conversion is biased towards warmer areas on the landscape, then habitat loss may confound the effects of climate change on a species range [8]. Studies evaluating the relative effects of habitat loss and climate change so far indicate that habitat loss remains a more important population driver than climate change for many species [9,10], although this may be changing in some systems [11]. Both factors can lead to shifts in species ranges [12,13], but the response of species' distributions to shifting contributions of these threats over broad timescales is less certain.…”

Navigating the pitfalls and promise of landscape genetics

“…Spear and Storfer ; Gabrielsen et al . ; Reid & Peery ). Despite the fact that many studies estimate gene flow for just one species on a single landscape, results are often presented as broadly generalizable landscape effects likely to apply to areas outside of the study or across taxa.…”

Population dynamics of endangered blanding's turtles in a restored area

“…The negative effects of habitat loss and fragmentation on this species are compounded by the continuing encroachment of other anthropogenic pressures. Blanding's turtles are particularly vulnerable to road mortality because of their propensity for long‐distance overland movements (e.g., Beaudry et al , Steen et al , Reid and Peery ). In addition to reduced adult survival, many Blanding's turtle populations experience high rates of nest depredation, potentially because of increases in synanthropic mammalian nest predator populations (Congdon et al ) and edge effects (Temple ).…”